The present invention relates to electronic postage meters, and more specifically to an electronic postage meter having multiple non-volatile memories(NVMs) for storing different historical information reflecting postage transactions.
Various electronic postage meter systems have been developed, as for example, the systems disclosed in U.S. Pat. No. 3,078,457 for Microcomputerized Electronic Postage Meter Systems, U.S. Pat. No. 3,938,095 for Computer Responsive Postage Meter, European Patent Application No. 80400603.9, filed May 5, 1980, for Electronic Postage Meter Having Improved Security and Fault Tolerance Features, U.S. Pat. No. 4,301,507, for Electronic Postage Meter Having Plural Computing Systems, and copending application Ser. No. 447,815, filed Dec. 8, 1982, for Stand-Alone Electronic Mailing Machine.
Generally, electronic postage meters include some form of non-volatile memory capability to store critical postage accounting information. This information includes, for example, the amount of postage remaining in the meter for subsequent printing and the total amount of postage already printed by the meter. Other types of accounting or operating data may also be stored in the non-volatile memory, as desired.
However, conditions can occur in electronic postage meters where information stored in non-volatile memory may be lost. A total line power failure or fluctuation in voltage conditions can cause the microprocessor associated with the meter to operate erratically and either cause erasure of data or the writing of spurious data in the non-volatile memory. The erasure of data or the writing of spurious data in the non-volatile memory may result in a loss of critical accounting information. Since the accounting data changes with the printing of postage and is not permanently stored elsewhere, there is no way to recapture or reconstruct the lost accounting information. Under such circumstances, it is possible that a user may suffer a loss of postage funds.
To minimize the likelihood of a loss of information stored in the non-volatile memory, various approaches have been adopted to insure the high reliability of electronic postage meters. It is known from aforementioned U.S. Pat. No. 3,978,457 and aforementioned co-pending application Ser. No. 447,815 to provide a microprocessor controlled electronic postage meter having memory architecture which includes a temporary storage memory for storing accounting data reflecting each meter transaction and a non-volatile memory to which the accounting data is transferred during the power down cycle of the meter.
Another approach for preserving the stored accounting data has been the use of redundant non-volatile memories. One such redundant memory system is disclosed in patent application Ser. No. 343,877, filed Jan. 29, 1982, in the name of Frank T. Check, Jr., and entitled Electronic Postage Meter Having Redundant Memory. With such redundant memory system the two redundant non-volatile memories are interconnected with a microprocessor by way of completely separated data and address lines to eliminate error conditions. The data stored in each memory is the same, although the data may be stored in a diffcrent form in each memory, e.g., it may be coded. The data is applied to the memories simultaneously or sequentially at different times during the postage transactions.
Another redundant memory system is disclosed in the aforementioned European Patent Application No. 80400603.9. In such patent application, the same accounting data is written into each of the two non-volatile memories, designated BAMs, by updating the specific registers of the BAMs twice during each postage meter transaction, once in temporary form and once in permanent form to minimize the loss of accounting data during microprocessor failure.
The aforementioned redundant memory systems store the same accounting data in both non-volatile memories and do not store "permanent" historical information of the postage transactions or provide a sequence of individually addressable memory locations to provide a historical record or audit trail for each postage transaction.